Question

An element 'x' has mass number 4 and atonic number 2.write electrons,protons,neutrons present in it and its valency.

Answer 1

Since we know that
Atomic number = no. Of electrons
or protons
Given
2 = no. Of electrons and protons
Now
Atomic mass = no. Of protons + no of
neutrons
4 = 2 + no. Of neutrons
4-2 = neutrons
2 = neutrons
Now valency
2 is complete d therefore valency is 0


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Answer 2

The element 'x' is Helium.
No. of -
Electrons - 2
Protons - 2
Neutrons - 2

As helium belongs to the zero group or the noble gases, its valency is zero. Another reason for it being zero, is that its first shell is completely filled.